The invention relates to the field of optical communication, and in particular to a photonic crystal ribbon-beam traveling wave amplifier.
The third-generation (3G) wireless communication standards call for hardware-based upgrade to the second-generation (2G) Global Systems for Mobile Communications using Wideband Code Division Multiple Access (W-CDMA) and Universal Mobile Telephone System (UMTS) as well as software-based upgrade to 2G Code Division Multiple Access (CDMA). The 3G wireless communications require amplifiers operating frequencies that are 1.12 to 3 times that of present frequencies, which are in the range from 900 MHz to 1700 MHz.
In general, the bandwidth of a transmitter, which is the most important figure of merit, increases with the central frequency of the amplifier. However, the number of transmitting towers must increase as the square of the central frequency, while keeping the power of the transmitting tower at a constant. This is because the distance between two adjacent transmitting towers is inversely proportional to the frequency. For example, if 1-GHz transmitting towers have a spacing of 10 miles, then 2-GHz transmitting towers must have a spacing of 5 miles. In other words, four 2-GHz transmitting towers are required to cover 100 square miles, whereas only one 1-GHz transmitting tower is needed for the same area.
Moreover, the total RF power per unit area increases with increasing data rate. For example, 3G wireless networks are expected to have considerably higher data rate than 2G wireless networks. As a result, the number of power amplifiers increases more dramatically than the square of the carrier frequency.
In order for the third-generation (3G) and future wireless communications to be a viable business, it is essential for the telecommunication equipment industry to provide ultra-low-cost amplifiers.
At present, most wireless base stations are powered by solid-state power amplifiers, which operate with efficiencies in the 8-12% range. The cost of solid-state amplifier is about $100/Watt. The cost of power amplifiers per base station at 1.5 kW is $150,000. For the RF power part of a wireless base station, the operating cost is comparable to the capital cost, because of the low operating efficiencies and heat removal.
Conventional helix traveling wave tubes (TWTs), which are not employed in any existing wireless base stations, cannot meet the ultra-low-cost requirement set by any potential third-generation wireless infrastructure provider. For example, a 100 W, 2 GHz conventional helix TWT costs $20K a piece or more.
There is a need to develop high efficiency, low-cost microwave amplifiers for 3G and future wireless base stations.